Propeller blade pitch setting device



Patented July 26, 1938 UNETED STATES PROPELLER BLADE PITCH SETTINGDEVICE Walter W. Burrington, Seattle, Wash., assignor to Northwest AirService Inc., Seattle, Wash, a corporation of Washington ApplicationFebruary 11, 1936, Serial No. 63,310

Claims.

This invention relates to propeller blade pitch setting devices and aprimary object of this invention is to provide a propeller blade pitchsetting device of simple and efficient construction 5 which. is quicklyand easily applicable to a propeller blade and which will save a greatdeal of time and labor in imparting a proper pitch to a propeller blade.

Another primary object of this invention is to provide a propeller bladepitch setting device which is adapted to be mounted on a propeller bladealone without being connected to any other support and which is operableto twist or pitch said propeller blade in either direction and whichleaves said propeller blade free to assume its natural angle when notorque is being exerted on said pitch setting device thus making itpossible to obtain a correct measurement of the pitch of the propellerblade without disconnecting, or loosening the pitch setting device.

Another object is to provide a propeller blade pitch setting devicecomprising two relatively strong frame members pivotally connectedtogether for relative angular movement, said two frame members beinginterconnected by power step-up means by which they may be angularlymoved relative to each other and each of said frame members beingprovided with means for engaging a propeller blade, said two bladeengaging means being spaced from each other.

A further object of the invention is to provide a propeller blade pitchsetting device which is equally well adapted for initially putting thecorrect pitch in a propeller blade or for restoring the correct pitch toa propeller blade which has been damaged.

In the methods heretofore commonly employed of imparting pitch to metalairplane propeller blades by exerting a torque or twist on the blades ithas been common practice to use clamping devices engaging the propellerblade at two locations and to secure one of said clamping devices to afixed support or have the same held by an operator while the otherclamping device is being angularly moved to twist or pitch the blade.This method consumes a great amount of time because it is oftennecessary to twist the blade and then measure the pitch angle of theblade several times at one station before 50 the correct pitch isobtained and obviously it is necessary to disconnect a fixedly securedclamping device either from the blade or from its support and relievethe blade from strain each time before the pitch angle can be correctlymeasured. Where two operators are used, one

on each clamping device, it has also been found necessary to disconnectthe blade clamping devices, which are usually in the nature of longlevers, before the pitch angle of the blade can be correctly measured.

This invention overcomes the objectionable features hereinbefore pointedout by providing a propeller blade pitch setting device which issupported on the propeller blade only and is not secured to any othersupport and which is positioned so that it does not affect the pitchangle of the blade when no torque is being exerted by the pitch settingdevice.

Other and more specific objects of the invention will be apparent fromthe following description taken in connection with'the accompanyingdrawing.

In the drawing Fig. 1, is a side elevation of a propeller blade pitchsetting device constructed in accordance with my invention.

Fig. 2 is a front elevation of the same.

Fig. 3 is a plan view of the same.

Fig. 4 is a sectional View substantially on broken line 44 of Fig. 2. 1

Fig. 5 is a somewhat diagrammatic side elevation on a smaller scaleshowing this propeller pitch setting device applied to a propellersupported on a pitch table.

Like reference numerals designate like parts throughout the severalviews.

This device embodies a channel shaped frame member having a base portion6, a side portion 1, and a top portion 8. Another frame member,hereinafter termed a front frame member, is operatively positioned atthe open side of the channel shaped frame member. This front framemember consists of a relatively strong base por tion 9, two uprightportions It and an arcuate top portion H. The base portion 9 of saidfront frame member is pivotally connected by a pivot bolt I2 with thebase portion 6 of the channel shaped frame member. As there is verylittle strain on this pivot bolt l2 said bolt may be of relatively smalldiameter. The base portion 9 of the front frame member is of strong andsubstantial construction and is preferably provided on its bottom sidewith two rigidly connected propeller blade engaging plates [3 of metalwhich is softer than the metal ordinarily used in the construction ofpropellers. A transverse clamp bar H! has its two end portions connectedwith the base portion 9 of the front frame member by bolts E5. The uppersurface of the bar I4 is preferably curved to conform, in a general way,

to the transverse curvature of a propeller blade 29, Fig. 2, and ispreferably provided with two rigidly secured propeller blade engagingplates it of soft metal positioned opposite to the plates l3. The platesI3 and I6 being of softer metal than the propeller blade will not marthe propeller when they contact the same. When the device is in use on apropeller blade the nuts on the bolts IE will preferably be tightenedjust enough to lightly clamp the blade and yet permita slight slippageof the blade between the plates l3 and It as a twist or pitch is putinto the a blade.

The rear portion of the channel shaped frame member, at the junction ofthe base 6 and side i, is provided with an integral transverse barportion ll which is connected with a clamp bar it by bolts l9 andcooperates with said clamp bar a propeller blade. Opposed plates 20 ofsofter material are secured to the bar portion I7 and clamp bar l8 so asto engage with the propeller blade and avoid marring the same.Preferably the plates I3 and i6 which cooperate with the front framemember and the corresponding plates 2% which cooperate with the channelshaped frame member are positioned so that they engage with thepropeller blade inwardly from the edges thereof. This avoids injury tothe thin edges of propeller blades. Also it provides a propeller bladeengaging means which has sufficient contact with propeller blades of thedifferent widths and transverse curvatures usually encountered to adaptthis device for use on blades covering a wide range of sizes.

Power multiplication or step-up means is provided for angularly movingthe two frame members relative to each other. One preferred powermultiplying or step-up means is in the form of a gear segment 2! securedto the arcuate top portion 5 l of the front frame member and meshingwith a gear pinion 22 secured to a stub shaft 23 which is jcurnaled inthe top portion 8 of the channel shaped frame member and in an L shapedbracket 24 which is rigidly secured to the channel shaped frame memberby screws 25. The L shaped bracket 24 extends partially around the gearsegment 2! and arcuate top portion II of the front frame member andforms a guide and support and completes a structure which securely holdsthe gear segment 2i in mesh with the pinion 22. This structure alsopermits free angular movement of the two frame members relative to eachother. The stub shaft 23 has an integral portion positioned above thechannel shaped frame member and this integral portion preferably is ofsquare cross section for engagement within a square opening in the endof a lever arm 26. A tube 27 may be slipped over the end of the leverarm 28, as shown in Fig. 5, to provide any desired length of lever arm.

In the operation of this device a propeller which is to be bent to apredetermined pitch or which is to have its pitch altered or correctedis placed on a horizontal pitch table 28 with its hub portion securedupon an upright axle member 3E which is rigidly mounted on the pitchtable 28 near one end thereof and extends upwardly from the tableat'right angles thereto. This positions and holds the axis of thepropeller at right angles to the table and makes it possible to measurethe pitch of the blades relative to the horizontal top of the pitchtable. In setting the pitch of a propeller it is common practice to readthe pitch at intervals of six inches on the IE) to form a clamp forsecurely clampingpropeller blade and for this reason it is preferable tomark off the pitch table at intervals of six inches by marks 3| shown inFig. 5. In restoring the proper pitch to a bent or damaged propeller thepropeller is first straightened longitudinally to restore the properalignment. Said propeller is then mounted on the upright axle member 30so that one blade which is to be straightened is positioned above thepitch table 28 and the other blade extends beyond the end of the pitchtable. The pitch setting device is then placed on the blade to bestraightened, usually by slipping it over the end of said blade, thechannel shaped frame member being nearest to the hub of the propeller.Starting at a station on the propeller blade nearest to the hub of thesame and usually about eighteen inches from said hub, the pitch of theblade is measured with a protractor and if the pitch at this station isfound to be wrong the pitch setting device is positioned with the bladeengaging elements of the front frame portion at this station and theother set of blade engaging elements between this station and the hub.The blade engaging elements ll and I8 are then clamped tightly on theblade and the blade engaging elements 9 and i5 clamped somewhat looselyon the blade. The operator who is correcting the pitch of the blade thenpreferably stands in a position so that he can hold another blade of thepropeller to prevent the .propeller from turning on the axle 30 and atthe same time angularly move the lever 26 in either desired direction toexert the desired twisting and bending force on that portion of thepropeller between the two clamps. As the propeller is bent or twisted atany station it may be checked from time to time with a protractor toascertain whether or not the correct angle for this station has beenattained. This checking can be done without loosening the clamps orremoving the pitching device, as said pitching device is not connectedto anything except the propeller and does not exert any twisting strainon the propeller when the lever 2621 is released.

As soon as the proper pitch is imparted to the bladeat one station thepitch setting device is moved outwardly on the blade to the next stationand the process repeated. By working from the hub portion of thepropeller outwardly it is possible to accurately pitch all of thestations on a blade in a short period of time. Also it is found thatafter the pitch of a station is properly set, such pitch will not bedisturbed by the setting of subsequent stations, due to the fact thatthe cross sectional area and strength of the propeller blade decreasesfrom the hub toward the tip.

From the foregoing description it will be seen that this pitch settingdevice is supported entirely on the blade which is being pitched duringoperation and is not secured to the pitch table 28 or to any fixedsupport. For this reason the part of the blade which is being set willalways assume its natural angle when no torque is being exerted on thepitch setting device and the angle of the blade may always be measuredwithout disconnecting the pitch setting device or loosening the clamps.

The foregoing description and accompanying drawing clearly shows apreferred embodiment of my invention but it will be clearly understoodthat this disclosure is merely illustrative and that such changes in theinvention may be made as are within the scope and spirit of thefollowing claims.

I claim:

1. Propeller blade pitch setting devices for use on a propeller which issupported on a pitch table With a blade thereof in close proximity tothe table comprising two frame members; pivotal means connecting saidtwo frame members for relative angular movement; blade engaging meansconnected with each of said frame members and positioned external tosaid frame members and at one side of said frame members and adjacentthe pivotal connection of said frame members and adapted to receive andhold a propeller blade which is positioned in close proximity to thepitch table whereby the pitch of the blade may be measured withreference to the table; and frame member moving means operativelyconnected with said two frame members for relatively moving said framemembers angularly in opposite directions.

2. In a propeller blade pitch setting device, for use on a propellerwhich is supported on a pitch table with a blade thereof in closeproximity to the table, a channel shaped frame member; blade clamp meansconnected with one end of said channel shaped frame member; a frontframe member pivotally connected with said channel shaped frame member;blade clamp means connected with an end of said front frame member inspaced relation from said blade clamp means on said channel shaped framemember said two blade clamp means being adapted to receive a propellerblade which is positioned externally of said two frame members and inclose proximity to the pitch table; and frame member moving meansoperatively connecting said two frame members whereby said two framemembers may be relatively moved angularly in opposite directions ontheir pivotal connection.

3. In a propeller blade pitch setting device, for use on a propellerwhich is supported on a pitch table with a blade thereof in closeproximity to the table, a channel shaped frame member having a baseportion an upright portion and a top portion, another frame memberpositioned at the front of said channel shaped frame member insubstantially parallel spaced relation to the upright portion of saidchannel shaped frame member; pivot means connecting the bottom portionsof said two frame members permitting relative angular movement of saidtwo frame members; power step-up devices interconnecting said two framemembers for angularly moving the same; and two spaced apart propellerblade clamping devices connected with the bottom portions of therespective frame members externally of said frame members.

4. In a propeller blade pitch setting device, a channel shaped framemember having a base portion an upright portion and a top portion;another frame member positioned at the front of said channel shapedframe member in substantially parallel spaced relation to the uprightportion of said channel shaped frame member; pivot means connecting thebottom portions of said two frame members permitting relative angularmovement of said two frame members; a gear rack secured to one of saidframe members; a gear pinion rotatably mounted on the other frame memberand operatively meshed with said gear rack; gear pinion rotating meansconnected with said gear pinion; propeller blade engaging meansconnected with the lower portion of said front frame member; andpropeller blade clamp means connected with the lower portion of saidchannel shaped frame member in spaced relation from the propeller bladeengaging means on the front frame member.

5. In a propeller blade pitch setting device, a channel shaped framemember having a base portion an upright portion and a top portion;another frame member positioned at the front of said channel shapedframe member in substantially parallel spaced relation to the uprightportion of said channel shaped frame member; pivot means connecting thebottom portions of said two frame members permitting relative angularmovement of said two frame members; a gear rack secured to said frontframe member; a gear pinion mounted on the top portion of said channelshaped frame member and meshing with said gear rack; a bracket securedto said channel shaped frame member extending over said gear racksupporting said gear rack for movement; gear pinion rotating meansconnected with said gear pinion; propeller blade engaging meansconnected with the lower portion of said front frame member; andpropeller blade clamp means connected with the lower portion of saidchannel shaped frame member in spaced relation from the propeller bladeengaging means on the front frame member.

WALTER. W. BURRINGTON.

